The individual effect of four human antibiotics on the microalgae Raphidocelis subcapitata was investigated following a 120-h exposure. The effects were assessed by analyzing growth, and biochemical parameters related with: 1) antioxidant capacity and oxidative damage by measuring superoxide dismutase (SOD) activity and lipid peroxidation (LPO) levels; and 2) cellular energy allocation (CEA) by quantifying the content in energy reserves, which represents the energy available (Ea), and the electron transport system activity that represents a measure of oxygen and cellular energy consumption (Ec). Growth yield inhibitory concentrations of sulfamethoxazole (18–30%), clarithromycin (28.7%), ciprofloxacin (28%) and erythromycin (17–39%) were found to elicit a considerable increase in Ec, thereby causing a significant decrease in the CEA. The elevated Ec can be a result of the need to respond to oxidative stress occurring under those conditions given the significant increase in SOD activity at these levels. For sulfamethoxazole, erythromycin and ciprofloxacin, the antioxidant responses do not seem to be enough to cope with the reactive oxygen species and prevent oxidative damage, given the elevated LPO levels observed. A stimulatory effect on growth yield was observed (up to 16%) at ciprofloxacin lowest concentration, which highly correlated with the increase in CEA. Based on the no observed effect concentration (NOECs) and/or effective concentration (EC₁₀) results, Ec, SOD and CEA were more sensitive than the classical endpoint of growth rate for all the tested antibiotics. By revealing the antibiotic stress effects in R. subcapitata at the cellular level, this study suggests CEA as a more reliable indicator of the organisms’ physiological status.

暴露120小时后，研究了四种人类抗生素对小藻类Raphidocelis subcapitata的单独作用。通过分析生长和与以下相关的生化参数来评估其影响：1）通过测量超氧化物歧化酶（SOD）活性和脂质过氧化（LPO）水平来测定抗氧化能力和氧化损伤；2）通过量化能量储备中的含量来表示细胞能量分配（CEA），该能量表示可用能量（Ea），而电子传输系统活性则表示氧气和细胞能量消耗的量度（Ec）。发现磺胺甲恶唑（18–30％），克拉霉素（28.7％），环丙沙星（28％）和红霉素（17–39％）的生长抑制浓度引起Ec的显着增加，从而引起CEA的显着降低。 。高架EC鉴于这些条件下SOD活性显着增加，可能是由于需要应对在这些条件下发生的氧化应激所致。对于磺胺甲恶唑，红霉素和环丙沙星，鉴于观察到的LPO水平升高，抗氧化剂的反应似乎不足以应付活性氧并防止氧化损伤。在环丙沙星最低浓度下观察到对生长产量的刺激作用（高达16％），这与CEA的增加高度相关。根据未观察到的作用浓度（NOECs）和/或有效浓度（EC ₁₀）结果，对于所有测试的抗生素，Ec，SOD和CEA均比经典的增长率终点更为敏感。通过揭示抗生素的应力作用在细胞水平上，亚次生拟南芥（R. subcapitata）认为CEA是生物体生理状态的更可靠指标。